It would likely be due to the release of Engine 1.55 where we refactored shader chunks to help pave the way to supporting the glTF material extensions and standardising the Chunk API.
Chances, this issue is caused by this specific issue where we fixed Index of Refraction to be applied correctly to the material when it wasn’t before in 1.54 and below.
See this link for more details: https://forum.playcanvas.com/t/engine-release-v1-55-0/26663#my-models-look-to-shiny-or-blown-out-9